There was a related feature request for TFTP server functionality recently.
Having a TFTP server would potentially allow the ability to serve a PXE boot image to network clients.
More specifically, via chainloading, it becomes possible to expand PXE netboot functionality by serving a PXE ROM that contained gPXE or iPXE, which further allows more expansive netboot functionality via supporting other protocols beyond TFTP.
gPXE is the old standby for PXE environments, but apparently it is no longer actively maintained. iPXE is a fork of gPXE that is being maintained.
Having iPXE baked in allows interesting things like being able to do spot work on PC's such as cloning or inspection using a netboot liveCD style image that iPXE can call on (Clonezilla being an example)
Necessary prerequisites are at a minimum a TFTP server and a DHCP server that provides netboot information such as TFTP server location where iPXE is located. iPXE documentation indicates there are some DHCP server tweaks necessary to prevent boot loops and BIOS/UEFI differentiation.
Possible secondary issues are linkages between VyOS DHCP settings and TFTP server listening addresses (if registering a TFTP server location for DHCP that is VyOS' TFTP server, rather than an independent TFTP server located elsewhere)
A tertiary issue is how to add light customization of iPXE operations via its native scripting. There is the suggestion of using a HTTP based script generator for the native dynamic script functionality.
But apparently this seems to be a recommended method now that is all iPXE native scripting
The following seems to be an ISC DHCPD config for doing the BIOS/UEFI differentiation
There is also a related note about some OS (for example Windows PE) boot faster delivering the image over HTTP, which would suggest some sort of HTTP server/TFTP server directory overlap might be helpful (but that may require HTTP without SSL?).
There is a final note regarding broken TFTP client implementations and a mitigation.